JP2006509569A - Pulsation durability test method and apparatus for tube graft - Google Patents

Abstract

A method for testing the pulsatile endurance of a vascular implant 3 comprises placing a resilient insert 4 into the implant and repeatedly expanding and contracting the insert, thereby expanding and contracting the implant. The insert preferably has a cavity therein and is repeatedly expanded and contracted by repeatedly increasing and decreasing the pressure in the cavity.

Description

  The present invention relates to a pulsation durability test method and apparatus for a tube graft.

  Artificial tube grafts such as heart valves, stents, grafts, and stent grafts that are used for transplantation into the human body are subjected to stress that varies continuously depending on blood pressure. As such, such implants need to be tested to verify durability over the entire period of use exposed to pulsating blood pressure.

  In many prior art documents, breaking an inelastic container (such as a glass bottle) by inserting an elastic insert such as an air bag into the container and applying an extremely high inflation pressure to the air bag until the container breaks (See, for example, US 3,895,514, GB 2,177,220, GB 1,531,557, and GB 2,149,126). None of these methods are suitable for pulsatile testing of tube grafts.

  Commercially available tube graft pulsation testing devices can be obtained from suppliers such as Enduratec Inc and Dynatec Dalta. These comprise one or more elastic tubes in which the implants are placed. The tube is filled with a liquid, usually saline, and the pressure in the tube is changed by a pump. Different types of pumps are used, some researchers prefer positive displacement mechanical pumps, while others prefer to drive the piston directly with an electric linear motor

  The progress of fatigue depends on a first rising liquid pressure inside the tube that causes the tube to expand and a second falling liquid pressure that can cause the tube to contract. As the tube expands, the graft expands with the tube due to the radial elasticity of the graft. When the tube contracts, the graft is squeezed by the tube and restored to its original dimensions.

  A similar method is disclosed in DE 199 03 476 (Inst. Implantatechnologie), which relates to a test method for vascular grafts in which the vascular graft is placed in an elastic sheath and external pressure is applied to the vascular graft. .

  These have a number of common failures and difficulties associated with placing the graft within the tube.

  The most serious commercially is that the tube will burst during the test. In many environments, a catheter or similar tube is used to insert the graft into the tube. The graft is first crushed prior to insertion of the catheter, and this crushing process has a significant impact on the average life of the graft. Thus, if the tube fails during the test, the tube itself can be replaced, but it is inappropriate to retransmit the graft through the catheter. This is because it involves a second crush of the graft into the catheter, resulting in a reduction in the average life of the graft. Graft replacement costs are rarely significant. However, endurance testing usually lasts for 3-6 months, and such failures can easily delay testing and product launch by months.

  As a result of failure modes such as those described above, test equipment designers typically employ tubes that are particularly thin and sturdy. The compliance of such tubes (ie the rate of increase in diameter per unit pressure) is relatively low and is used for tube expansion to achieve physiologically typical diameter changes. The pulsating pressure applied is usually significantly higher than the physiological pressure. For example, the blood pressure in the abdominal aorta in an average healthy person is 120 mm Hg / 80 mm Hg, that is, the blood pressure changes by 40 mm Hg for each pulsation. The compliance of a healthy aorta is about 5% per 100 mm Hg, and a diameter change of 2% is expected for each heartbeat. In order to simulate such a change in diameter, some researchers have employed pulsating pressures between 80 mm Hg and 100 mm Hg.

  When the graft has a large surface across the vessel, such as a tapered stent or stent graft, the force per unit area along the axial direction of the graft increases in proportion to the inflation pressure of the tube. This high pressure causes failure modes such as limb separation or movement that do not occur under physiological pressure.

  A drawback in existing designs not related to the above-mentioned failure is that it is limited to the form of the tube. Stent grafts are often designed to be used in branch vessels, and branch test tubes are required for their testing. Stent grafts are also used in aneurysms. Thus, if the tube is qualitative, each part of the graft will contact the inner wall of the tube, but if the tube is an aneurysm, the graft will pass through the void. In addition, affected tubes are often highly winding. Because of these, a tube that branches, has different compliance at different sites, can be an aneurysm, and is highly twisted must be available. Such a composite tube product is possible, but difficult, expensive and time consuming.

  A further problem in endurance testing is due to the requirement for full life testing over a commercially reasonable period. In general, tube grafts are tested for 400,000,000 cycles corresponding to a transplant life of about 10 years at a heart rate of 80 beats / minute. Many companies have tested large grafts at about 35 Hz and can complete the test in about 19 weeks.

  In order to reduce the time it takes to bring a new product to the market, it is desirable to increase the test speed as much as possible. However, the test methods described above have frequency limitations due to radial elasticity and graft surface area. This occurs by the following mechanism.

  As the pressure in the tube increases, it moves away from the graft wall. Due to the radial elasticity of the graft, the wall of the graft follows the wall of the tube. However, this elasticity is not sufficient to overcome the frictional resistance of the fluid through which the graft wall passes, so that the graft wall may move slower than the tube wall. Thus, greater resistance reduces radial elasticity, increases test speed, and causes the tube graft to be delayed with respect to movement of the tube wall. In these situations, the strain generated in the graft is reduced with increasing frequency, and changes in the diameter of the graft are no longer compatible with changes in the diameter of the tube.

  The present invention is directed to an improved arrangement for testing tube grafts that overcomes or minimizes all of the above limitations.

  As a first aspect of the present invention, an elastic insert is prepared, the insert is inserted into a tube graft, the insert is repeatedly expanded and contracted, and thereby the graft is expanded and contracted. A method for testing the pulsation durability of a tube graft is provided.

  The insert may be mechanically expanded and contracted (including, for example, an expandable stent), but preferably the insert has a cavity therein and by repeatedly increasing or decreasing the pressure in the cavity. It is repeatedly expanded and contracted. The frequency of expansion / contraction is preferably at least 25 Hz, more preferably 25-100 Hz, and particularly preferably 50-100 Hz.

  As an improved technique, it is preferable to employ a tube disposed inside the tube graft. The tube can be formed of an elastic material such as latex rubber, silicone rubber, polyurethane or similar materials. The tube is preferably made to have a very thin wall so that the inflation pressure in the tube is transmitted directly to the inner surface of the graft during the test. In fact, a contraceptive condom is an ideal tube for testing large implants.

  Such a configuration has the advantage that if the tube breaks during the test, the replacement tube can be inserted through the graft without fear of damage to the graft. In this way, it is not necessary for the test graft to become defective due to tube failure, and the time spent up to the moment of failure is not lost.

  A second advantage of such a configuration is that physiological pressure can be used in the tube because the walls are very thin and the pressure decay is very low.

  A third advantage of such a system is that the tubes can be separated because the mechanical properties of the tube surrounding the implant under test can be varied at different sites, and the outer tube does not have to seal the fluid. It can be formed with parts. This eliminates the need for the entire tube to be made of the same material and allows the compliance of different sites to be optimized.

  A fourth advantage of such a system is that the inner tube is very soft, which allows a sharp curve or bend of the test implant, not simply a custom, but simply by restraining the bent tube. Become.

  A fifth advantage of the system is that the test frequency can be increased because the implant expands from the inside rather than relying on radial elasticity. When used in combination with an outer tube, the aforementioned system provides for compression of the graft due to the elasticity of the outer tube, in addition to a positive graft inflation drive method. The movement of the wall of the graft does not depend much on the characteristics of the graft alone, and the test can be performed at 50 Hz to 100 Hz. At this rate, 400 million cycles can be completed in 7 weeks.

  Graft diameters compatible with such devices are in the range of 2 mm to 50 mm. Nonetheless, the inner test tube can be significantly smaller or larger than standard if it has a sufficiently thin wall.

  The wall thickness of the inner tube is preferably in the range of 0.03 to 0.2 mm. Although performance is reduced, some advantages of the inner tube can still be obtained if the wall thickness is a few millimeters.

  A preferred way to obtain a high insert expansion / contraction frequency is to use a modulator such as a rotary valve or oscillating piston that modulates continuously supplied air into a series of pulsations having the required frequency. .

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
1 includes a support (1), an infusion tube (2), a tube graft (3), an inner tube (4), an outer short tube (5) that reduces compliance at the neck of the graft, a stopper (6 ) And (7).

  In this configuration, an ultrathin wall condom is employed as a pair of inner tubes (4) packed into the single body portion of the implant (3) and its two legs. Plugs (6) and (7) are used to limit the vertical expansion range of each tube so that higher pressures can be used in the tube (4). At each outlet to the tube graft (3), this restriction is within the portion of the outer tube that continues to the tube graft. In this way, there is no path for the inner tube to expand or escape beyond the tube sample or outside the outer tube. This limits the maximum strain in the inner tube and prevents the inner tube from bursting unless very high pressure is used.

  A further improvement employed in this configuration is that compressed air is used as the pressurized medium for the inner tube. A rotary valve or oscillating piston can be used to pulsate the air pressure, and the design of such a valve or piston is very simple because only the air pressure needs to be adjusted. Other researchers using saline filling systems generally require a pressure modulator that acts directly on the saline solution with erosion and leakage problems.

  A rotary valve (known as a pulser) consists of a cylindrical housing in which a rotating cylinder is housed. The cylinder has two holes that are orthogonal to its rotation axis and pass through it. They form a right angle and are axially offset from one another along the axis of rotation. The housing is parallel and has two holes that pass through it, which are axially aligned with the holes of the cylinder.

  As the cylinder rotates, the lateral holes are alternately connected to and displaced from the lateral holes of the housing. When connected to the exhaust connection, pressure is released. Therefore, the condom repeats pressurization and decompression as the cylinder rotates. Pressure pulsation can be adjusted by the initial air pressure, the size of the exhaust hole, and the rotational speed of the cylinder.

  A further advantage of employing air for system pressurization is that the amount of oscillating fluid is significantly reduced compared to using saline. In other words, the power required for the modulator system is reduced.

  Even when a compressed air system is employed, it is preferable to keep the tube graft at physiological temperature and in saline. If the outer tube is discontinuous, the implant can be held in saline by placing the entire system in a saline bath at the appropriate temperature.

  With large implants, the volume change per pressure pulsation (pulse) can be increased, which increases the demand for the modulator. In this regard, a compressed air system is preferred over a liquid filling system because gas is more compressible. To reduce the amount of gas in such a system, the inner tube can be partially filled with water, or a smaller diameter tube can be used.

FIG. 1 shows an apparatus configuration configured for testing a branch graft according to the present invention.

Claims (21)

  A method for testing the pulsation durability of a tube graft, comprising preparing an elastic insert, inserting the insert into a tube graft, and repeatedly expanding and contracting the insert, thereby expanding and contracting the graft. .   The method of claim 1, wherein the insert has a cavity therein and the insert is repeatedly expanded and contracted by repeatedly increasing and decreasing the pressure in the cavity.   The method according to claim 1 or 2, wherein the insert is a flexible tube sealed at one end.   The method according to any one of claims 1 to 3, wherein a thickness of a wall portion surrounding the cavity in the insert is 0.03 to 0.2 mm.   The method according to any one of claims 1 to 4, wherein the insert is made of latex rubber, silicon rubber or polyurethane.   6. The method according to any one of claims 1 to 5, wherein the insert comprises a contraceptive condom.   The method according to any one of claims 1 to 6, wherein the frequency of expansion and contraction of the insert is 50 to 100 Hz.   The method according to any one of claims 1 to 7, wherein the intracavity pressure is increased by pressurizing fluid into the cavity.   The method of claim 8, wherein the fluid is air or saline.   The method according to claim 1, wherein at least a part of the graft is immersed in saline.   11. A method according to any one of claims 1 to 10, wherein the graft is a branched graft and at least two inserts are used, one for each branched branch.   The method according to any one of claims 1 to 11, wherein the graft is a tube graft having an inner diameter of 2 to 50 mm.   13. A method according to any one of claims 1 to 12, wherein the test is carried out continuously over a period of about 7 weeks.   14. A method according to any one of the preceding claims, wherein the graft contraction is made solely by the inherent elasticity of the graft.   Prepare an elastic outer sheath, place at least a portion of the graft within the sheath, and during the expansion of the graft, the graft compresses the sheath, and in addition to the inherent elasticity of the graft, The method according to any one of claims 1 to 13, wherein a contractile force is applied to the graft.   The method of claim 15, wherein the sheath body is formed of the same material as the insert.   Including an elastic insert having a cavity therein and means for repeatedly expanding and contracting the insert by repeatedly increasing and decreasing the pressure in the cavity, thereby repeatedly expanding and contracting the implant into which the insert is inserted in use , Tube graft pulsation durability test equipment.   The apparatus of claim 17, wherein the insert is a flexible tube sealed at one end.   19. A device according to claim 17 or 18, wherein the means for repeatedly increasing or decreasing the pressure in the cavity is such that the frequency of expansion and contraction of the insert can be 50-100 Hz.   The apparatus according to any one of claims 17 to 19, wherein the means for repeatedly increasing and decreasing the pressure in the cavity is a compressed air source.   21. The sheath of claim 17-20, further comprising an elastic outer sheath having at least a portion of the implant disposed therein, wherein the sheath provides contraction when the implant is expanding against the sheath. The apparatus of any one of Claims.

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